ErrorProne: BluetoothMapbMessage

remove unused variable and empty tag
+
```
533: warning: [EmptyCatch] Caught exceptions should not be ignored
                    } catch (IOException e) {
                      ^
788: warning: Return value of 'replaceAll' must be used
                data.replaceAll("([/]*)/END\\:MSG", "$1END:MSG");
                               ^
789: warning: Return value of 'trim' must be used
                data.trim();
                         ^
968: warning: Avoid having multiple unary operators acting on the same variable in a method call
            value = data.substring(j++, ++j);
                                  ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: I35de374a7085fcc7e04d0678089d74b97c83c63d